Journal of Hazardous Materials B139 (2007) 373–380 Electrocoagulation of synthetically prepared waters containing high concentration of NOM using iron cast electrodes Yalc ¸ın S ¸evki Yildiz a,∗ , Ali Savas ¸ Koparal b ,S ¸ ahset ˙ Irdemez a ,B¨ ulent Keskinler c a Department of Environmental Engineering, Atat¨ urk University, 25240 Erzurum, Turkey b Department of Environmental Engineering, Anadolu University, 26470 Eski¸ sehir, Turkey c Department of Environmental Engineering, Gebze Institute of Technology, Engineering Faculty, 41400 Gebze, Turkey Received 4 February 2006; received in revised form 13 June 2006; accepted 14 June 2006 Available online 18 June 2006 Abstract The aim of this investigation is to evaluate the treatibility of synthetically prepared water with high concentration of humic substances by electrocoagulation in batch mode using iron cast electrodes. Effects of applied potential, initial humic substance concentration and supporting electrolyte type on humic substance removal efficiency were investigated. NaNO 3 , Na 2 SO 4 and NaCl were used as supporting electrolyte. Among these supporting electrolytes, Na 2 SO 4 and NaCl have provided high removal efficiencies, whereas in the experiments using NaNO 3 as supporting electrolyte have been observed no flock formation. The highest removal rate is obtainable with NaCl as supporting electrolyte. Removal efficiencies for initial humic substance concentration of 500 mg L −1 with NaCl and Na 2 SO 4 equal to 97.95% for 35 min and 92.69% for 70 min, respectively. This behavior of the system has been derived from oxidation products, available in the bulk solution, of chloride ions. When NaCl is used as supporting electrolyte, there is an advantage of providing the disinfection of water, but humic substances and chloride ions are available in the bulk solution with risk of formation undesirable organo-chlorine compounds, so the Na 2 SO 4 is the most favorable supporting electrolyte. © 2006 Elsevier B.V. All rights reserved. Keywords: Electrocoagulation; Humic substances; Iron cast electrodes 1. Introduction Given the substantial content of aromatic and aliphatic residues present in humics and the relatively small content of ionisable carboxylic groups, the humics are easily aggregated and precipitated on charge neutralization. In the broadest terms the structures can be described as assemblies of covalently linked aromatic and aliphatic residues carrying carboxyl, pheno- lic and alkoxy groups although sulphate esters, alanine moieties, semiquinone, phosphate ester and hydroquinone groups have been proposed to exist in some humic isolates [1]. Humics are believed to be formed from plant and animal residues by microbial decay by the process of humification, which occurs in soils, sediments and natural waters. Given the long time span of the biodegradation of the organic precursors and the exposure of the products to water, oxygen and radia- tion (sunlight) in the environment, humics must be regarded as ∗ Corresponding author. Tel.: +90 442 2314799; fax: +90 442 2360957. E-mail address: ysevki@yahoo.com (Y.S ¸. Yildiz). ‘old molecules’ which are at the end of the biodegradative and oxidative route [1] humic substances are close to being non- biodegradable and are the end-point of nature’s biodegradation [2], thus it is believed that possibly cannot undergo much further breakdown unless exposed to specific chemical agents which they have not previously encountered [1]. Their presence has been a problem in the water industry and in environmental purification. These problems can be summarized as follows. During the chlorination, natural organic matters (NOMs) cause formation of disinfection-by-products (DBPs). Tri- halomethanes are the well known disinfection-by-products (chloroform, bromo-dichloromethane, chloro-dibromomethane, and bromoform) [3–8]. It has been suspected that some of the trihalomethanes (especially chloroform) are carcinogenic com- pounds [3–9]. They lead to color, taste and odor in waters [4,7,8]. NOMs stimulate the regrowth of the microorganisms in water distribution systems [4,7,8]. Availability of micro-pollutants and heavy metals associated with NOMs [4,7]. The contamination of humic substances has been known to induce a deterioration of adsorbents and a prevention of adsorption onto the adsorbents. 0304-3894/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2006.06.044